This invention relates to a direct fuel injection system for an internal combustion engine.
The advantages of direct cylinder injection are well known. Basically, by employing direct cylinder fuel injection with an internal combustion engine it is possible to obtain increases in fuel economy and exhaust emission control. The reason for this is that it is substantially easier to obtain fuel stratification with direct injection systems and fuel stratification can achieve the aforenoted results. However, one difficulty with providing for fuel stratification in the combustion chamber is that it must be ensured that the stoichiometric fuel patch is at the spark gap at the time it is fired. This is a considerable problem, particularly at low speeds and low loads.
With one type of direct cylinder fuel injection which has been employed, the fuel is injected at a relatively low pressure (approximately ten times atmospheric pressure). Because of this low pressure of fuel injection, the fuel must be injected relatively early in the induction cycle so as to avoid the problems of injecting the fuel once the mixture becomes compressed in the combustion chamber. Once compression takes place, the pressure difference between the low pressure fuel injector and the area where it injects is not enough to permit sufficient fuel flow.
Another problem with direct cylinder injection employing such low pressures is that the size of the injection nozzle must be relatively large so as to insure adequate fuel is injected during the period when injection takes place. If large enough diameters are employed to accommodate the high speed, high load conditions of the engine, then the injector nozzle size is so large that at low speed, low loads, the fuel particles become quite large and complete atomization of the fuel is not possible.
It is, therefore, a principal object of this invention to provide an improved arrangement for injecting fuel directly into the cylinder of an engine wherein adequate amounts of fuel can be injected under all conditions and good vaporization will result.
A form of combustion chamber has been proposed that will improve fuel stratification and in which a recess or bowl is formed in the head of the piston and a projection extends into this recess. The concept of employing a projection into the recess is that the fuel is desired to be sprayed in proximity to this projection and this will ensure vaporization of the fuel. However, with this type of arrangement it is difficult to ensure that the vaporized fuel will be around the gap of the spark plug at the time it is fired. The reason for this is that, as already noted, it is normally the practice to spray the fuel into the cylinder at a time well before top dead center and the fuel charge can easily be dispersed out of the recess into the remainder of the combustion chamber to form a mixture that is too lean for firing or, alternatively, not juxtaposed to the spark gap at the time the spark plug is fired. With the previously proposed type of arrangement it has been necessary to delay the start of firing of the spark plug in relation to the total time of fuel injection from the fuel injection valve. This is done so as to permit the fuel evaporated from the projection to reach the spark plug at the time when the spark plug is fired. This system has been utilized with four cycle engines.
However, the application of this type of principle to a two cycle engine gives rise to problems which cannot be solved with the type of arrangement applied to four cycle engines. In a two cycle engine, the temperature within the combustion chamber after compression is higher and the temperature of the head of the piston is also higher. Thus, fuel that is injected evaporates faster than with a four cycle engine and the kinetic energy created by its evaporation and expansion rapidly dissipates. Because of this, the mixture which has been sprayed against the projection in the combustion chamber can readily dissipate before it reaches the spark plug and also the loss of kinetic energy can result in incomplete combustion. In addition, two cycle engines require good scavenging and the scavenging action can disturb the fuel stratification.
Because of the aforenoted situations, it is extremely important when applying direct cylinder injection to a two cycle engine that employs a projection on the head of the piston to improve stratification to place the spark plug gap as close as possible to the piston projection. An arrangement has been disclosed in the commonly-assigned application for United States Letters Patent entitled "Cylinder Fuel Injection Type Two-Cycle Internal Combustion Engine", Ser. No. 08/012,311, filed Feb. 2, 1993, in the names of the inventors of this application and also of Seiichi Nishimura and in its parent application of the same title, Ser. No. 07/830,670, filed Feb. 3, 1992, now abandoned, to provide a system and method for injecting fuel into the engine against the projection so that the better combustion can occur and also that stratification may be achieved at low speed, low load conditions.
In addition, with this type of combustion chamber it is also extremely desirable to insure that a large percentage of the fuel injected, particularly at low speed, low load conditions, will actually impinge upon the projection. Thus, in addition to the problems of proper fuel capacity and particle size, with this type of combustion chamber it is also important to insure that the injector nozzle is configured so that a large portion of the injected fuel will be sprayed onto the projection at low speed, low load conditions.
It is, therefore, a further principal object of this invention to provide an improved direct cylinder injection system for an internal combustion engine that achieves fuel stratification and ensures firing, even under low load, low speed conditions.
It is a further object of this invention to provide an improved fuel injector nozzle arrangement for the type of engine having a combustion chamber with a projection onto which the nozzle sprays and which will insure that maximum amounts of fuel particles at the right size will be sprayed onto the projection, particularly at low speed, low load conditions.